For most Tyranid players, gaunts form the bread-and-butter of any Tyranid army. Their strength lies in their capacity for rediculous numbers, and swarm-armies are very powerful.
Personally, I've always been a fan for variety. The idea of having nothing but gaunts makes me cringe, not only in a "boring" sense, but in a very daunting sense. Painting this many models becomes more of a chore than a hobby. Rather, I'm attempting to put together a 3,000 point Tyranid army that utilizes a variety of the different models, yet still retain some of those numbers.
For my theme, I disliked all the color-schemes I saw in books ... save one. In the old Warhammer 40k v.3 rulebook, there's maybe 2 pictures of some Tyranids colored with purple skin and black carapaces. This, by far, looked the coolest to me ... and it also didn't conflict with any color schemes I had planned for the other armies. (For example, I had considered making my Eldar Biel-Tan, but their color is green ... and I've got Dark Angels.)
When I painted up a few Tyranids back in v.3, I ended up liking the color scheme for the most part. My problem was that their faces weren't showing, and the Tyranid faces are the scariest part of the model! I want these guys to freak out their enemies! I tried a few tactics to bring the faces more to life and settled on using red as an accent color. It makes the faces vivid, and even implies that they're bloody. Awesome. Bloody awesome.
Fast forward a few years, v.4 has been out, I decide to make this blog and make all my armies using the new v.4 codexes and models.
Lots of my Tyranids bit the dust... and for the better. Pretty much across the board I like the v.4 models better than the v.3 or earlier. I did a search for the various Hive Fleets, and stumbled across a reference to a "Hive Fleet Harbinger" who are described as having "purple flesh with black carapaces." Awesome. So my 'nids are a splinter fleet from Hive Fleet Harbinger, distinguishable from the rest by their Blood Red faces.
Ok, back to the termagaunts (sorry for the back-story-rant). I have planned two broods of termagaunts, 8 models each. I know, this is small. There is a reason, though. Despite having the tools available to make a "shooty Tyranid" army, I felt their potential leaned much more towards the "close combat" side of battle. With this in mind, I built my army to maximize on close combat ... with very minor ballistic potential.
One Termagaunt brood will be equipped with Fleshborers, the other with Devourers. No biomorphs. I had considered "endless numbers" but the Termagaunts just aren't important enough to me. These two broods are available to me, mainly as backup and as tactical place-holders. Need to capture something (ala 'Take and Hold')? Why divert one of my costly units to hold something when I have this cheapy unit for that very purpose? The rest of my army rushes forward and ties my opponent in melee, while these little buggers simply play 'King of the Mountain.'
Don't think I'm making a huge mistake by sacrificing numbers, though. I am fully aware of that huge benefit and necessity to the Tyranids. I intend on filling those numbers with other units than Termagaunts, though. Hormagaunts, now that's more like it! In the works are two broods of Hormagaunts (16 each), one biomorphed and one not. 10 Ripper Swarms. 16 Genestealers. 16 Gargoyles. 12 Raveners. 6 Warriors. 3 Lictors. Tyrant with 3 guards. Broodlord. 2 Zoanthropes (with synapse creature as well as Warp Blast) and a bio-morphed to high-hell Carnifex. Seriously, this guy's The Juggernaut.